In the next year we hope to accomplish the following three projects: 1. To complete the hormone profile of pregnancy by assaying LH and prolactin in the serum, and reassaying estrogen levels. 2. To determine if the rat blastocyst produces a substance from the trophoblastic cells. This chronic gonadotropin could potentially act in two ways; it could be LH-like or more prolactin-like. The LH-like action can be assessed by adding blastocysts to dissociate cell preparations of Leydig cells and measuring the testosterone synthesized per blastocyst. A similar amplification system, employing dissociated cells from newly formed corpora lutea, can be employed in the search for a prolactin-like product. In this system the luteal cells would be preincubated with blastocysts of a given age and then varying amounts of LH would be added to the incubating cells. In theory a prolactin-like substance eminating from the blastocyst would elevate the progesterone/20 OHP ratio. This ratio would be compared to that of cells not incubated with blastocysts. 3. We will continue to search for the best dosage of steroids for maintenance for pregnancy. However, there may be need to change the sequence of administration or the mode of delivery. Currently, we are considering the use of Silastic tubing containing steriods. The tubing packed with steriod can be cut to any length and can be implanted subcutaneously. A predetermined length of tubing will deliver a steroid continuously at a given rate. This avoids sharp daily increases in hormones, the result of injection and may mimic normal physiology more closely.